The present study aimed to understand the relationship among family function, depressive mood and Internet addiction among senior high school students. Additionally, we examined the mediating role of depressive mood in the relationship between family function and Internet addiction. This study recruited 2,170 high school and technical school students through purposive sampling (high school students: 51.94%; males: 47.87%). Administered questionnaires included the Family Function Scale – short form, Ko’s Depressive Inventory, and Chen Internet Addiction Scale. Findings showed the following: (a) the average Internet usage time per week was 13.42 hours (SD 15.43 hours), including an average of 11.22 hours (SD 14.29 hours) for non-academic purposes; (b) poor family function significantly predicted Internet addiction; (c) depressive mood significantly predicted Internet addiction; (d) poor family function significantly predicted depressive mood; and (e) depressive mood partially mediated the relationship between poor family function and Internet addiction. Findings from the present study provide suggestions and a reference for schools and guidance counselors, as well as for future research.